Conventionally, a water tank system and a dry-type load system using a metal resistor have been used for carrying out load characteristic tests of a power generator.
For load characteristic tests about 20 years ago, a water tank system has been mainly used wherein three electrodes are suspended from above such that a potion of the electrode is submerged in an electrode-water-filled tank having a vertical length of 2 m, a horizontal length of 2 m, and a height of 1.5 m and wherein a continuous power conditioning is performed while adjusting the submerged length of the portion.
In such a water tank system, however, increase of power consumption causes a temperature rise of the electrode water. When the temperature of the electrode water reaches about 75° C. under a high voltage condition, arc discharge starts to take place. Thus, in order to suppress such arc discharge, there have been attempts to decrease the temperature of the electrode water by frequent supply of cool water. With this, however, as cool water is supplied, a large amount of water which has been increased in temperature up to about 75° C. must be drained accordingly. The volume thereof reaches as much as 16 m3 per hour.
In order to solve the problem with the drainage of hot water caused by the aforementioned water tank system, the present inventor used, as a load characteristic test method not using electrode water, a load characteristic test method disclosed in commonly-owned Japan Patent No. 1462423 wherein a pure-water resistor that is a load device system is used. The pure-water resistor comprises a cylindrical base electrode, a main electrode passing through the bottom of the base electrode, and an insulating cylindrical sheath disposed between these electrodes, wherein electrode water between these electrodes is used as a resistance for consuming electric power and therefore continuous load adjustment is ensured.
According to this method, the electrode water heated to a high temperature is cooled by a blower and water spray and then recycled. As a result, the amount of water consumption can be reduced to as small as one-tenth of the water consumption amount required for the aforementioned water tank system, and a beneficial effect that the drainage of industrial water is made unnecessary is achieved.
Such a load device system using a pure-water resistor has an advantage that a continuous load adjustment is provided without draining hot electrode water. However, similarly to the water tank system, the use of such a system requires a large amount of electrode water for operating the system. Further, when the system operating environment is, for example, a norther province environment or the like, there is a risk that the electrode water is frozen under a below-zero environment during wintertime. Thus, the maintenance thereof would take more time and effort.
As described above, in a facility where a hot water cannot be processed or where water supply is difficult to be secured, a load device using a dry-type metal resistor can alternatively be used as a device for load adjustment without using electrode water. However, this is not a complete solution because a metal resistor is poor in insulation performance, and therefore it often includes such a risk factor that the metal resistor itself burns.
In order to solve the aforementioned problem, the present inventor developed, as disclosed in Japanese Patent Application No. 2003-193358, a dry-type high-voltage load system wherein a resistor element is supported by an insulating sheath suitable for an operating voltage, as a result of which unexpected arc discharges and chain breaking between resistor elements are suppressed and firing of a metal resistor is prevented.